Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is prior art, nor that such background art is widely known or forms part of common general knowledge in the field.
Optically-pumped semiconductor vertical-external-cavity surface-emitting lasers (VECSELs) have evolved rapidly during the past decade. An extensive discussion is contained in M. Kuznetov, Semiconductor Disk Lasers: Physics and Technology. Wiley Online Library. Chap. 1 (2010). VECSELs are a very versatile type of laser, because a wide range of semiconductor materials can deliver a selection of emission wavelengths and tenability, and because the open cavity design enables easy integration of intracavity components and nonlinear processes. From a single VECSEL, the direct emission has ranged from violet at 390 nm [2] to mid-infrared [3], and output powers up to 40 W output power have been reported to date [4].
Intracavity second harmonic generation (SHG) is well established as a means of substantially expanding the spectral coverage of VECSELs, and the yellow region is one that has been particularly targeted [5]. Intracavity-doubled VECSELs also benefit from the short carrier life time in semiconductors (typically a few ns) and the lack of spatial hole burning in the periodic gain structure, and therefore their output has low amplitude noise. This is in contrast to the so-called “green problem” [6], in which longitudinal-mode competition often causes strong intensity noise in intracavity doubled conventional solid-state lasers. Other intracavity second-order nonlinear processes that have been reported for VECSELs are optical parametric oscillation [7] and difference frequency generation [8].
Recently, Parrotta et al. has demonstrated a VECSEL-pumped intracavity continuous-wave (cw) Raman laser [9], in a new approach to combine the tunability from VECSELs with wavelength shifting from stimulated Raman scattering (SRS). They pumped a KGW crystal within a VECSEL cavity and shifted the fundamental emission around 1.06 μm to 1.14 μm with a tunable range from 1133-1157 nm.